Control of the secondary crystallisation process in poly(hydroxybutyrate-co-hydroxyvalerate) through the incorporation of poly(ethylene glycol)

Poly(hydroxybutyrate-co-hydroxyvalerate) (PHB-co-HV) is a sustainable and biodegradable polymer, but as a potential packaging material, it suffers from a narrow processing window and embrittlement over time due to secondary crystallisation. This study aims to extend previous research by exploring the effect of the addition of poly(ethylene glycol) (PEG), in a range of molecular weights and compositions, on the rate of embrittlement. On blending, it was apparent that there was a reduction in both the melting point (of up to 7 degrees C) and the melt viscosity. Furthermore, there was a reduction in both the modulus and tensile strength indicating that PEG acts as an effective plasticiser in PHB-co-HV. In terms of the secondary crystallisation process, the addition of PEG could not prevent the process from occurring, only hinder it. PEG 600 in relatively high concentrations was found to be the most effective in this regard with a 53% reduction in the change in Young's modulus compared to pure PHB-co-HV. This observation, together with the melting point reduction which extends the processing window for PHB-co-HV, makes PEG a worthwhile additive to an otherwise fundamentally brittle polymer.